.text
.global  _start
_start:

//设置栈
        ldr sp,=0x80200000

        bl clean_bss

        bl main

halt:
        b halt

clean_bss:
        /* 清除BSS段 */
        ldr r1, =__bss_start
        ldr r2, =__bss_end
        mov r3, #0

clean:
        str r3, [r1]
        add r1, r1, #4
        cmp r1, r2
        bne clean

        mov pc, lr